1. Field of the Invention
The present invention relates to a noise reduction device, more specifically, a noise reduction device for use in a backlight module of a liquid crystal display (LCD).
2. Descriptions of the Related Art
Due to the advantages of slimness, power-saving and low radiation, liquid crystal displays (LCDs) have been widely applied in consumer electronic products. A direct-type backlight module is frequently employed in the illumination technology of an LCD. The main structure of the LCD generally comprises two portions, namely, a panel module and a backlight module. The panel module primarily includes an indium-tin-oxide (ITO) conductive glass substrate, liquid crystal layer, alignment film, color filter, polarizer sheet, and driving integrated circuits (IC). The backlight module mainly includes a light source, a light guide plate, a brightness enhancement film (BEF), a diffusion sheet, a reflection sheet, and an optics-film. Because the panel module is not luminous, it needs the backlight module to furnish visible lights to make the display operate under a normal condition.
In the direct-type backlight module, a cold cathode fluorescent lamp (CCFL), an external electrode fluorescent lamp (EEFL), or a light emitted diode (LED), can be selected as the light source. As an example, FIG. 1 illustrates a conventional cold cathode fluorescent lamp (CCFL) for use in a back light module. The backlight module includes a back bezel 10, two lamp holders 20, a reflector sheet 30, and a plurality of CCFLs. 40. The back bezel 10 comprises a rectangle back plate and four side plates disposed around the rectangle back plate to constitute a frame structure and to form a receiving space (often referred to as the light box) within the frame structure. Moreover, the two lamp holders 20 are independently fixed onto two opposing side plates of the back bezel 10. The reflector sheet 30 is disposed above the back plate of the back bezel 10. The plurality of lamps 40 are disposed in the light box of the back bezel, with both ends of each lamp 40 fastened by the two lamp holders 20 so that the lamps 40 can be fixed above the reflector sheet 30 for projecting lights to an optical component (not shown) of the backlight module.
With reference to FIG. 2, a partially enlarged view of the upper-left area of the subject in FIG. 1, the back bezel 10, lamp holders 20, reflector sheet 30, lamps 40 and their interrelated positions are clearly shown. In consideration of cost, dimension and insulation effects, plastic material is always used for making the lamp holder 20 of the backlight module; however, the plastic material varies in dimension depending on the temperature change, especially in response to the operation or non-operation of the light-box. The back bezel 10 which is often made of metal material, such as aluminum (Al), iron (Fe), or the like also bears similar variation tendencies due to temperature changes. This phenomenon causes the lamp holders and the back bezel to change dimensions themselves, affecting the dimensions of the gap formed between these two structures. In the worst case scenario, these two structures would come into contact with each other intermittently to cause a well known “pop noise”.
FIG. 3 shows a conventional fastening technology of lamps and lamp holders. In this figure, a plurality of fastening elements 50 are engaged onto the lamp holders 20 (also shown in FIG. 2). Each of the fastening elements 50 comprises a recess for receiving the end of each of the lamps. By means of engaging each fastening element 50 to the lamp holder 20, the lamps 40 could easily engage onto the lamp holders 20. It is understandable that FIG. 3 only shows the schematic view of one side of the backlight module. In an actual embodiment, the quantity of the fastening elements 50 would correspond to that of the lamps 40.
Conventional technology resolves the above-mentioned pop noise using two major measures. One is that the originally designed gap between the back bezel 10 and the lamp holders 20 can be increased to a size greater than the existing deformation generated by the back bezel 10 and the lamp holders 20 under possible thermal expansion and cold contraction. In this case, the back bezel 10 would not come into contact with the lamp holders 20, and therefore the concerned pop noise can be avoided. However, there are still other unexpected problems. Specifically, the increasing gap allows undesired dust to leak through. In other words, although increasing the gap between the back bezel 10 and the lamp holders 20 can solve the pop noise problem due to temperature change, the gap can worsen the dust leakage problem. This dust leakage problem is of great concern, which is a quite concern in the LCD design field. The other measure taken to avoid the pop noise is to apply a sticker stripe that has a double-faced adhesive between the back bezel 10 and the lamp holders 20. Although this arrangement can somewhat make up for the aforementioned dust leakage problem, it makes the assembly process more complicated and is not cost and time effective.
Given the above, it is critical to create an inventive design in a backlight module that is capable of resolving the pop noise that generates between the lamp holders and the back bezel due to operational temperature changes. In addition, this design could avoid undesired dust leakage between the holders and back bezel, while providing a simple manufacturing and assembly process.